Tsukasa Tameyasu

Intracellular potentials in the small cells and cellular interaction in the cardiac ganglion of the lobster Panulirus Japonicus

Abstract o 1. The electrical activity in the lobster cardiac ganglion was studied by means of intracellular microelectrodes, attention being focused on membrane potential changes in the small cells. 2. In many cases the small cell produced a periodic burst of spikes superimposed on a slow potential. 3. The synaptical interaction was observed among the small cells. 4. Most of the small cells innervated the large cells. 5. Intracellular stimulation of the small cell was effective in inducing the burst of discharges in the ganglion.

Unloaded shortening after a quick release of a contracting, single fibre from crayfish slow muscle

SummaryThe time course of shortening at zero load was studied by the slack test method during tetanic contractions in isolated, single, slow muscle fibres of the crayfish. In 28 of 32 shortenings (from 14 different fibres) a biphasic shortening was seen, which consisted of an initial high-velocity phase lasting 3.3–20.8 ms and a following slow-velocity phase lasting for the entire time examined (up to 89.2 ms). Provided that the shortening occurred uniformly along the fibre length, velocity in the initial phase, V1, of the biphasic shortening was 14.4±3.4 (mean±SD,n=10) μm s−1 per half sarcomere at Lo, the slack length, at 20°C, while that in the second phase, V2, was 7.4±1.4 μm s−1 per half sarcomere. Lowering temperature decreased both V1 and V2 with Q10=1.4 for V1 and 2.0 for V2. Lowering the external Ca concentration from 15 mM, the standard, to 2 mM resulted in a tetanic tension below one-third of that at 15 mM Ca and decreased both V1 (t test; p<0.01) and V2 (p<0.001). Prestretching the fibre to 1.5 Lo had no significant effect on V2 (p<0.3) but increased V1 (p<0.001). The distance shortened during the initial high-velocity phase, LV1, was 4.0±1.8% Lo (mean±D,n=10) at 20°C or about 0.14 μm per half sarcomere on average. LV1 was independent of the tetanic tension level when it was changed by lowering the external Ca concentration or temperature in the same fibre. Prestretching the fibre to 1.5 Lo, at which the sum of the active and the resting tension was lower than Po at Lo in two of three fibres, increased LV1 significantly (p<0.001). The independency of LV1 from the tension level indicates that the initial high-velocity phase was not from shortening of some inert components in the fibre. One possibility is that the initial high-velocity phase was brought about by an acceleration of shortening by a compressive force, the origin of which has been discussed. The slow-velocity phase seemed to result from the crossbridge turnover with little exogeneous stress on myofilaments. Four different fibres exhibited an unloaded shortening with a constant velocity during the entire time examined (29.9–61.8 ms). This type of shortening had a velocity between the usual V1 and V2 values, suggesting that a compressive force accelerated the shortening during the entire time.

Velocity of free shortening and elasticity in glycerinated molluscan smooth muscle

Abstract 1. 1. Velocity of free shortening ( V 0 ) and elasticity of the glycerinated anterior byssal retractor muscle (ABRM) of Mytilus were examined by applying length steps during contractions at pCa 6.3 and 6.5. 2. 2. The highest V 0 obtained during the rise of active force at pCa 6.3 was 0.77 L 0 /sec at 20°C, the value comparable to that in frog twitch fibers if expressed as the sliding velocity between thick and thin filaments. 3. 3. The amount of elastic shortening required to reduce an active force to zero level was less than 2% of the fiber length, which was greater than that estimated by extrapolating back the shortening curve to the time of the length step.

Acceleration of Ca2+ Repletion in the Junctional Sarcoplasmic Reticulum and Alternation of the Ca2+-Induced Ca2+-Release Mechanism in Hypertensive Rat (SHR) Cardiac Muscle

We estimated the time taken for a repletion of the junctional sarcoplasmic reticulum (JSR) Ca(2+) stores from a family of mechanical restitution curves after twitches of various magnitudes in the cardiac muscle of hypertensive rats (SHR), using a method described previously (Tameyasu et al. Jpn J Physiol. 2004;54:209-19), to evaluate abnormality in Ca(2+) handling by cardiac JSR in hypertension. We found no differences in contractility or in the time course of mechanical restitution between SHR and the controls (WKY) at 3 weeks of age. In comparison to WKY, 7- and 20-week-old SHR showed a greater rested state contraction (RST) and similar or smaller rapid cooling contracture, suggesting that their JSR contains a similar amount of Ca(2+) at saturation, but releases more Ca(2+) upon stimulation. The adult SHR and WKY showed similar mechanical restitution time courses, but the adults had longer pretwitch latencies. The function G(t) representing the time course of JSR Ca(2+) store repletion in adult SHR exceeded the WKY value at t < or = 0.5 s, but the function H(t) representing JSR [Ca(2+)] change corresponding to the mechanical restitution after RST was smaller in the adult SHR at t < or = 0.5 s, resulting in smaller H(t)/G(t) in adult SHR at t < or = 0.5 s. Deviations of G(t), H(t), and H(t)/G(t) from WKY were greater at 20 weeks than at 7. The results suggest an acceleration of JSR Ca(2+) store repletion and an alternation of the Ca(2+)-induced release of Ca(2+ )from the JSR in young adult SHR.