Table 1.

Influence of raised [Ca²⁺]_o (1.3 to 10 mM) on resting E_M and intracellular K⁺ activity at 11 mM [K⁺]_o in EDL muscle fibers

Parameter	4K	11K	11K + 10Ca
Surface fibers
EM, mV	−74.5 ± 1.7*	−55.0 ± 1.3*	−62.8 ± 1.1
aKi+, mM	124 ± 10	115 ± 4*	176 ± 8
EK, mV	−94.2 ± 1.9*	−66.9 ± 0.9*	−77.3 ± 1.1
EM − EK, mV	19.7 ± 1.3*	12.0 ± 1.2	14.5 ± 1.1
n	11/4	20/4	35/4
Layer 2 fibers
EM, mV	−82.2 ± 1.8*	−61.8 ± 1.6*	−68.4 ± 1.4
aKi+, mM	169 ± 13	144 ± 9*	202 ± 10
EK, mV	−101.7 ± 2.1*	−71.8 ± 1.7*	−80.7 ± 1.3
EM − EK, mV	19.6 ± 1.2*	10.0 ± 0.5*	12.2 ± 0.6
n	17/4	22/4	29/4

Values are means ± SE; n, no. of fibers/muscles. 4K, control Krebs solution with 4 mM K⁺, 1.3 mM Ca²⁺; 11K, raised K⁺ Krebs solution with 11 mM K⁺, 1.3 mM Ca²⁺; 11K + 10Ca, raised K⁺ Krebs solution with 11 mM K⁺, 10 mM Ca²⁺. Surface and layer 2 fibers were impaled from the same four extensor digitorum longus (EDL) muscles.

^*Significant difference (P < 0.05, unpaired t-test with Bonferroni correction) between 4K and 11K, or 11K and 11K + 10Ca. Changes of resting membrane potential (E_M), intracellular K⁺ activity (aK_i⁺), and K⁺-equilibrium potential (E_K) were also statistically significant at the individual muscle level (4–14 fiber impalements in each solution).