Existence of Q gamma in frog cut twitch fibers with little Q beta

• Published in: Biophysical journal Vol. 59; no. 2; pp. 503 - 507
• Main Authors: Chen, W., Hui, C.S.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01.02.1991; Biophysical Society
• Subjects: Animals; Biological and medical sciences; Electric Conductivity; Electrophysiology - methods; Fundamental and applied biological sciences. Psychology; Membrane Potentials; Molecular biophysics; Muscle Contraction; Muscles - physiology; Rana temporaria; Vertebrata; Electric charge; Frog; Sarcoplasmic reticulum; Membrane transport; Amphibia; Salientia
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(91)82243-3

Charge movements were measured in frog cut twitch fibers with the double Vaseline-gap voltage-clamp technique. In most fibers, when a depolarizing pulse to -60 to -40 mV was applied at 13–14 degrees C, the ON segment of a charge movement trace showed an early I beta component and a late I gamma hump component. An ongoing controversy is whether the I gamma hump component triggers calcium release from the sarcoplasmic reticulum or arises as a consequence of the release. Interestingly, a number of cut fibers showed normal I gamma components but greatly diminished, or unresolvable, I beta components. When the amount of charge associated with the current transient was plotted against the membrane potential, the steeply voltage-dependent Q gamma component appeared normal whereas the less steeply voltage-dependent Q beta component was also greatly diminished or unresolvable. These results suggest that I gamma can flow in the absence of I beta, thereby ruling out the possibility that Q beta triggers calcium release which, in turn, causes Q gamma to move. The results, however, do not rule out the positive feedback of calcium release to activate Q gamma, if calcium release is not triggered by Q beta but by Q gamma itself or by some other signal.