Clifford H. Wagner

Calcium Channel Agonist/Antagonist Effects on Cholinergic Stimulation of the Diabetic Rat Bladder

The in vitro effects of a calcium channel agonist (BAY K8644) and antagonist (nifedipine) on the cholinergic responses of the streptozotocin-induced diabetic rat bladder were investigated. the bladder body and bladder base were studied separately. There were significant differences in contractile responses to acetylcholine stimulation in the diabetic bladder body compared to the control body. Similarly, the diabetic bladder base demonstrated significantly increased contractile responses compared to the control base. Contractile responses in the diabetic bladder body and base were significantly increased from the control in the absence of extracellular calcium. Differences were found in the effects on maximum responses between diabetic and control tissues treated with nifedipine and BAY K8644. BAY K8644 did not completely reverse the effect of nifedipine on the contractile responses. Rates of contractile response were significantly different between controls and diabetics and between body and base. Alterations in calcium channel activity in diabetic bladder smooth muscle may be responsible at least in part for the nonspecific pharmacologic responses found in smooth muscle strips.

Neurogenic Function of the Diabetic Rat Bladder: Alteration by Calcium Channel Effectors

The in vitro effects of a calcium channel antagonist (nifedipine) and agonist (BAY K8644) on the neurogenic responses of the streptozotocin-induced diabetic rat bladder were investigated. The bladder body and bladder base were studied separately. There were no significant differences in neurogenic responses in diabetic bladder body compared to control body, but the diabetic bladder base demonstrated an increased contractile response at each frequency compared to control base. The rate of contractile response was similar in controls and diabetics but was significantly different between body and base. Although declining with time, contractile responses in the diabetic bladder body and base were increased from control in the absence of extracellular calcium. Differences were found in effects upon maximum responses between diabetic and control tissues treated with nifedipine and BAY K8644. BAY K8644 did not completely reverse the effect of nifedipine on the neurogenic responses in the diabetic bladder body. Effects of diabetes on the bladder body and base are associated with changes in calcium channel activity of bladder smooth muscle.

A Generic Approach to Iterative Methods

Iterative processes usually appear in the undergraduate curriculum as unrelated topics, each having a specific purpose and independent existence. Yet such topics as Newtons method, Picards method for showing the existence and uniqueness of solutions to initial value problems, the Economic Cobweb Theorem for describing supply and demand equilibria, the convergence theorem for the long-run behavior of regular Markov chains, as well as many other iterative processes, are simply different manifestations of the general theme set forth in the Contraction Mapping Principle. The first abstract setting for this principle is credited to Stefan Banach [2],[17],[27], who showed that, under a very general hypothesis, all sequences generated by the repeated evaluation of a distance-decreasing function must converge to a unique fixed point. This convergence is the essence of an iterative technique which can be used in a variety of applications to find an approximate solution, to assert that a unique solution must exist, or to show that a given sequence converges to a known solution. Such applications of the Contraction Mapping Principle are the substance of this article. A good example of a simple iterative process was shown to me by my five-year-old son Donald: Turn on a scientific calculator and repeatedly press the COS button. On a typical calculator, this algorithm computes iterated values of the calculator function COS(x), degree mode (a discrete rational function that approximates the continuous real function f(x)= cos(2 gx/360)), and displays successive terms of the sequence

Comparison of computerized cystometry/micturition and contractile responses of the diabetic rat bladder.

Computerized data acquisition was used to achieve a comprehensive assessment of micturition and cystometry in rats made diabetic with streptozotocin. Diabetic rats had a greater mean voided volume and a significantly shorter interval between voiding during the light cycle. During volume expulsion, the rate of intraluminal pressure development was greater, but the mean duration of volume expulsion was less in the diabetic bladder. The increased rate of intraluminal pressure development in the diabetic bladder at the time of volume expulsion correlated with the greater tension development in bladder body strips in response to acetylcholine stimulation. The inability of the diabetic bladder body to maintain peak intraluminal pressure may contribute to the development of residual urine, increased bladder volume and increased voiding frequency in the diabetic rat.