Carol L. Beck

Pore-forming segments in voltage-gated chloride channels

The ability to differentiate between ions is a property of ion channels that is crucial for their biological functions. However, the fundamental structural features that define anion selectivity and distinguish anion-permeable from cation-permeable channels are poorly understood. Voltage-gated chloride (Cl−) channels belonging to the ClC family are ubiquitous and have been predicted to play important roles in many diverse physiological and pathophysiological processes. We have identified regions of a human skeletal muscle ClC isoform that contribute to formation of its anion-selective conduction pathway. A core structural element (P1 region) of the ClC channel pore spans an accessibility barrier between the internal and external milieu, and contains an evolutionarily conserved sequence motif: GKxGPxxH. Neighbouring sequences in the third and fifth transmembrane segments also contribute to isoform-specific differences in anion selectivity. The conserved motif in the Cl−channel P1 region may constitute a ‘signature’ sequence for an anion-selective ion pore by analogy with the homologous GYG sequence that is essential for selectivity in voltage-gated potassium ion (K+) channel pores.

Aging-associated down-regulation of ClC-1 expression in skeletal muscle: phenotypic-independent relation to the decrease of chloride conductance

In order to clarify the mechanism underlying the reduction of resting membrane chloride conductance (g Cl) during aging, the levels of mRNA encoding the principal skeletal muscle chloride channel, ClC‐1, were measured. Total RNA samples isolated from tibialis anterior muscles of aged (24–29 months old) and adult (3–4 months old) rats were examined for ClC‐1 expression using Northern blot analysis, and macroscopic g Cl was recorded from extensor digitorum longus muscle fibers from each adult and aged rat in vitro using a two intracellular microelectrode technique. Although interindividual variability was observed, aged rats exhibited a parallel reduction of both g Cl and ClC‐1 mRNA expression as compared to adult rats. A linear correlation exists between individual values of ClC‐1 mRNA and g Cl. These results provide evidence that ClC‐1 is the main determinant of sarcolemmal g Cl and demonstrate that the decrease of g Cl observed during aging is associated with a down‐regulation of ClC‐1 expression in muscle.

Evaluation of Creatinine Clearance Estimation in an Elderly Male Population

Thirty‐one medically stable, elderly males (age 75 ± 8.3 yrs) participated in a prospective study evaluating the accuracy of 16 methods of estimating creatinine clearance. Serum creatinine values were determined on the mornings of days 1, 4, and 5 to assure stable renal function. On the morning of day 3, a 24‐hour urine collection was initiated. A statistically significant correlation existed between the measured and estimated clearance values for all 16 formulas. The correlation (r < 0.65) was lower than that in previously published studies, however. Five of the formulas (1A, 5A, 5B, 7A, 7B) demonstrated no statistical difference between mean measured and estimated values. In this population, formula 2B was the least biased and formula 9B the most accurate. For all 16 methods, the bias was minimal and the relative accuracy of the estimated methods was comparable. The results support using methods to estimate creatinine clearance only as a rough bedside prediction of renal function in elderly males.

Human Infection with Herpes Zoster: Etiology, Pathophysiology, Diagnosis, Clinical Course, and Treatment

Herpes zoster is a cutaneous vesicular eruption resulting from recrudescence of the chickenpox virus. It is mainly a disease of adults, with a predisposition for the elderly or immunocompromised. Although usually localized, the disease can disseminate to visceral organs. Diagnosis is often made based on the characteristic pattern of the lesion and clinical features. Tzanck smear, viral isolation, seroconversion, antibody titers, and monoclonal antibodies may further aid or confirm the diagnosis. Clinical features of herpes zoster may follow a progression through 3 stages, prodromal, acute, and chronic. The prodromal and acute phases seldom require more than symptomatic management. The chronic pain syndrome, postherpetic neuralgia (PHN), demands a more aggressive approach. Pharmacologic intervention, neuroaugmentation, and/or surgery may prevent or alleviate PHN, but universal response to any of these therapeutic approaches is unlikely. Tricyclic antidepressants remain the first choice in treating this pain syndrome. A trial of antiviral therapy may be warranted in patients with disseminated disease or in immunocompromised patients with localized disease. Of the antiviral agents, acyclovir is considered the drug of choice by most clinicians.

Patient tolerance to intravenous potassium chloride with and without lidocaine

Hypokalemia is a common electrolyte abnormality. Intravenous repletion therapy with potassium chloride (KCl) in concentrations > 80-100 mEq/L is not recommended due to patient intolerance. Since this guideline at times may be clinically impractical, this study was designed to examine use of peripheral vein infusions of high concentration KCl therapy. Tolerance to KG 20 mEq/65 ml iv with and without lidocaine 50 mg was evaluated in 18 hypokalemic subjects in a randomized, placebo-controlled, double-blind study. Subjective and objective assessments of adverse effects were determined throughout the infusion period. Pain was assessed by both verbal descriptor and visual analog scales and correlated significantly following infusion of KCl with or without lidocaine. Multivariant analysis demonstrated differences in pain perception between solutions, with significantly less pain following KCl with lidocaine versus KCl infusions. Transient adverse effects occurred in both groups, but the incidence was not statistically different. Use of concentrated iv KCl infusions may benefit hypokalemic patients with hypervolemia and/or severe potassium deficits. Addition of lidocaine clearly improves patient tolerance to intravenous KCl replacement.

Continuous Nasogastric Morphine Infusion

Morphine sulfate is the narcotic analgesic most commonly used for pain treatment in terminally ill patients. This case report demonstrates a new method of morphine administration. A 56-year-old terminally ill cancer patient with severe pain from metastatic adenocarcinoma of the lung required continuous nasogastric feeding and around-the-clock narcotic analgesics. The patient was safely and effectively converted from a continuous intravenous morphine infusion to continuous nasogastric morphine-enteral feedings. This method of administration may benefit patients receiving continuous enteral tube feedings who either require high-dose morphine therapy or are unable to use the oral administration route.

Evaluation of Therapeutic Drug Monitoring in a Long-Term Care Facility: A Pilot Project

The need for a therapeutic drug monitoring service was evaluated in a 150-bed long-term care facility. Thirty blood samples from 28 residents (mean age 87.9 years) were assayed to determine trough drug concentrations. All subjects were examined to determine pharmacodynamic effect. Pharmacokinetic consultations were written for serum drug concentrations outside accepted ranges. Fifty percent (15 of 30) of serum drug levels measured were subtherapeutic; the remaining levels were in the normal therapeutic range. Based on this sample data, it could be concluded that a minimum of 32 percent and as many as 68 percent of serum drug levels would be subtherapeutic following drug analysis in similar nursing home populations. Of 12 consultations, recommendations for seven (58 percent) were accepted by the subjects primary care physicians. Four of the consultations (33 percent) resulted in dosage modifications. These results support the need for further study.