Table 2.

Influence of raised [Ca⁺]_o (1.3 to 10 mM) on resting E_M and the profile parameters of single action potentials at 10 mM [K⁺]_o in surface fibers from soleus muscles

Parameter	4K	10K	10K + 10Ca
Resting EM, mV	−77.4 ± 1.6*	−56.2 ± 1.7*	−67.2 ± 1.2
Overshoot, mV	36.2 ± 1.2*	−20.3 ± 5.9*	21.9 ± 3.0
Amplitude, mV	113.6 ± 2.1*	35.3 ± 6.7*	89.1 ± 2.6
Width, ms	0.765 ± 0.017*	1.778 ± 0.120*	0.954 ± 0.044
Maximum +dV/dt, V/s	524 ± 22*	76 ± 18*	250 ± 22
Maximum −dV/dt, V/s	−174 ± 7*	−44 ± 9*	−115 ± 7
n	24/3	15/3	17/3

Values are means ± SE; n, no. of fibers/muscles. 4K data are pooled from before and after raised [K⁺]_o solutions. Action potentials were initiated via fine platinum wire (0.3 ms pulses). Peak tetanic force (125 Hz, 2 s) recovered from 41 ± 15% of control at 10K to 83 ± 7% of control at 10K + 10Ca in these three soleus muscles. Stimulation was with large transverse wire electrodes and supramaximal (10 V, 0.3 ms) pulses. +dV/dt and −dV/dt, peak and trough of the first derivative of the action potential, respectively.

^*Significant difference between 4K and 10K, or 10K and 10K + 10Ca (P < 0.05, ANOVA).