Contractile activation by voltage clamp depolarization of cut skeletal muscle fibres.

Abstract

SUMMARY1. Single frog skeletal muscle fibres bathed in a relaxing solution were cut close to the tendon and mounted across a single Vaseline gap so that a short segment of intact terminated fibre extended beyond one side of the gap.2. A compensating circuit, set with a micro-electrode in the terminated fibre segment, was used both to correct total current for external current crossing the gap and to correct pool voltage for the voltage drop across the fibre segment in the gap.3. The micro-electrode was then removed and the fibre voltage-clamped using the compensating circuit. This allowed movement without damage under controlled voltage.4. Strength-duration curves for contraction thresholds of cut fibres exposed externally to TTX Ringer solution and internally to a predominantly K glutamate solution were similar to strength-duration curves reported for intact fibres.5. The change from TTX Ringer to a predominantly (TEA)2SO4 external solution shifted the strength-duration curve for cut fibre contraction thresholds in the negative direction as reported for intact fibres.6. When studied at 3-4 00, fibres from warm-adapted frogs appeared to have higher contraction thresholds than fibres from cold-adapted frogs.7. Delayed rectifier currents recorded from cut fibres were similar to those reported for intact fibres.

Intramembranous charge movement in frog cut twitch fibers mounted in a double vaseline-gap chamber.

“…Movement in intact fibers was reduced by making the external solutions hyperosmotic with sucrose. The results with cut fibers were obtained with a single Vaseline-gap technique (Kovacs and Schneider, 1978) or a double Vaseline-gap technique , with internal and external solutions of normal osmolarity; movement was reduced by stretch, The last four rows in B give results from the experiments in this article. In columns 5-7, the values obtained without gap corrections were taken from Table V, columns 5-7 (SO 4) and from (Table VII A, columns 5 and 7).…”

Measurement and modification of free calcium transients in frog skeletal muscle fibres by a metallochromic indicator dye.

“…The procedures for preparing and mounting isolated cut segments of skeletal muscle fibres were generally similar to those used by Kovacs & Schneider (1978), except where modification was required for the double-gap system used in the present experiments. Ileofibularis or semitendinosus muscles were isolated from frogs (Rana pipien8) maintained at room temperature and fed on crickets.…”

“…Occasionally, the pool voltage or total current were recorded also. The fundamentals of the recording procedure have been described elsewhere (Chandler, Rakowski & Schneider, 1976;Kovacs & Schneider, 1978). Briefly, a voltage-to-frequency converter and a counter performed the analog-to-digital conversion.…”

“…The metallochromic indicator dye Antipyrylazo III (AP III) is convenient for use with our cut single skeletal muscle fibre preparations (Kovacs & Schneider, 1978; Kovacs, Rios & Schneider, 1979) because it diffuses into the fibre from the cut ends (Kovacs et al 1979;Kovacs & Szucs, 1980;Palade & Vergara, 1982). Arsenazo III, another metallochromic indicator which has been used for monitoring myoplasmic calcium transients in both intact (Miledi, Parker & Schalow, 1977;Baylor, Chandler 162 & Marshall, 1982b) and cut (Palade & Vergara, 1982) fibres, has been introduced by microinjection.…”

Kinetic properties of intramembrane charge movement under depolarized conditions in frog skeletal muscle fibers.

“…In this study we determined the charge movements in polarized and nonpolarized fibers using the single Vaseline-gap cut fiber technique of Kov~ics and Schneider (1978). The hyperpolarizing linear controls used conventionally for charge 1 determination contained considerably less charge 2 than in double or triple Vaseline-gap measurements Caputo and Bolanos, 1989).…”