Comparison of charge movement components in intact and cut twitch fibers of the frog. Effects of stretch and temperature

• Published in: The Journal of general physiology Vol. 98; no. 2; pp. 287 - 314
• Main Author: Hui, C S
• Format: Journal Article
• Language: English
• Published: New York, NY Rockefeller University Press 01.08.1991; The Rockefeller University Press
• Subjects: Animals; Biological and medical sciences; capacitance; Electrophysiology; Fundamental and applied biological sciences. Psychology; Homeostasis; Kinetics; membrane currents; Models, Biological; Muscle Contraction; muscles; Muscles - physiology; Physical Stimulation; Rana temporaria; Striated muscle. Tendons; Temperature; Vertebrates: osteoarticular system, musculoskeletal system; Temperature; Frog; Electric charge transfer; Amphibia; Electrophysiology; Salientia; Semitendinous muscle; Muscular fiber; Striated muscle; In vitro; Section; Vertebrata; Kinetics; Rana temporaria; Stretching
• ISSN: 0022-1295; 1540-7748
• DOI: 10.1085/jgp.98.2.287

Charge movements were measured in frog intact fibers with the three-microelectrode technique and in cut fibers with the double Vaseline gap technique. At 13-14 degrees C, the ON segments of charge movement records from both preparations showed an early I beta component and a late I gamma hump component. When an intact fiber was cooled to 4-7 degrees C, the time-to-peak of I gamma (tp,gamma) was prolonged, but I gamma still appeared as a hump. Q-V plots from intact fibers at 4-7 degrees C were fitted with a sum of two Boltzmann distribution functions (method 1). The more steeply voltage-dependent component, identified with Q gamma, accounted for 32.1% (SEM 2.2%) of the total charge. This fraction was larger than the 22.6% (SEM 1.5%) obtained by separating the ON currents with a sum of two kinetic functions (method 2). The total charge in cut fibers stretched to a sarcomere length of 3.5 microns at 13-14 degrees C was separated into Q beta and Q gamma by methods 1 and 2. The fraction of Q gamma in the total charge was 51.3% (SEM 1.7%) and 53.7% (SEM 1.8%), respectively, suggesting that cut fibers have a larger proportion of Q gamma:Q beta than intact fibers. When cut fibers were stretched to a sarcomere length of 4 microns, the proportion of Q gamma:Q beta was unchanged. Between 4 and 13 degrees C, the Q10 of l/tp,gamma in intact fibers was 2.33 (SEM 0.33) and that of 1/tau beta was less than 1.44 (SEM 0.04), implying that the kinetics of I gamma has a steeper temperature dependence than the kinetics of I beta. When cut fibers were cooled from 14 to 6 degrees C, I gamma in the ON segment generally became too broad to be manifested as a hump. In a cut fiber in which I gamma was manifested as a hump, the Q10 of l/tp,gamma was 2.08 and that of l/tau beta was less than 1.47. Separating the Q-V plots from cut fibers at different temperatures by method 1 showed that the proportion of Q gamma:Q beta was unaffected by temperature change. The appearance of I gamma humps at low temperatures in intact fibers but generally not in cut fibers suggests an intrinsic difference between the two fiber preparations.