Ca2+ current and charge movement in adult single human skeletal muscle fibres.

1. The Vaseline‐gap technique was used to record calcium currents (ICa) and charge movement in single cut fibres from normal human muscle. Experiments were carried out in 2 or 10 mM‐extracellular Ca2+ concentration ([Ca2+]o) and at 17 or 27 degrees C. 2. The passive electrical properties of the fibres with this technique were: membrane resistance for unit length rm = 59.4 k omega cm; longitudinal resistance per unit length ri = 4.9 M omega/cm; longitudinal resistance per unit length under the Vaseline seals re = 438 M omega/cm; specific membrane resistance Rm = 1.176 k omega cm2; input capacitance = 5.53 nF; specific membrane capacitance = 8.9 microF/cm2. 3. The maximum amplitude of ICa at 17 degrees C was: in 2 mM [Ca2+]o, ‐0.42 microA/microF and in 10 mM [Ca2+]o, ‐1.44 microA/microF. At 27 degrees C and in 10 mM [Ca2+]o, it increased to ‐3.04 microA/microF. The calculated temperature coefficient (Q10) for the increase in amplitude from 17 to 27 degrees C was 2.1. 4. Ca2+ permeability (PCa) was calculated using the Goldman‐Katz relation; in 2 mM [Ca2+]o at 17 degrees C, PCa = 1.26 x 10(‐6) cm/s; in 10 mM [Ca2+]o at 17 degrees C, PCa = 2.23 x 10(‐6) cm/s; in 10 mM [Ca2+]o at 27 degrees C, PCa = 4.03 x 10(‐6) cm/s. 5. The activation curve calculated from the PCa was shifted by 10 mV to positive potentials when raising [Ca2+]o from 2 to 10 mM. Increasing the temperature did not change the curve. The mid‐point potentials (Va 1/2) and steepness (k) of the activation curves were: at 17 degrees C, in 2 mM [Ca2+]o, Va 1/2 = ‐1.53 mV and k = 6.7 mV; in 10 mM [Ca2+]o, Va 1/2 = 9.96 mV and k = 6.8 mV; at 27 degrees C and 10 mM [Ca2+]o, Va 1/2 = 11.3 mV and k = 7.7 mV. The activation time constant in 10 mM [Ca2+]o reached a plateau at potentials positive to 10 mV, with a value of 93.8 ms at 17 degrees C and 17.4 ms at 27 degrees C. The calculated Q10 was 4.5. 6. The deactivation of the current was studied from tail currents at different membrane potentials in 10 mM [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)

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