Table 1

Activation of single purified skeletal muscle calcium-release channels by suramin at 20 to 100 μM activating Ca²⁺ and subactivating calcium concentration (0.6 and 0.05 μM).

		P_o	n
A	Control (20–100 μM Ca²⁺)	0.47 ± 0.04	9
	0.3 mM Suramin	0.72 ± 0.03	9
	0.6 mM Suramin	0.82 ± 0.04	6
	0.9 mM Suramin	0.87 ± 0.01	6
B	Control (50–100 μM Ca²⁺)	0.51 ± 0.05	5
	Control (0.6 μM Ca²⁺)	0.003 ± 0.001	5
	1.2 mM Suramin	0.050 ± 0.020	4
C	Control (50–100 μM Ca²⁺)	0.54 ± 0.02	6
	Control (0.05 μM Ca²⁺)	0.0008 ± 0.0004	6
	1.2 mM Suramin	0.018 ± 0.004	6
	1.2 mM Suramin ⁺ 80 μM 4-CMPS	0.81 ± 0.03	3

Single-channel currents were recorded at 0 mV holding potential (A) or⁺20 mV holding potential (B, C) with 480 mM/50 mM CsCl (cis/trans) and Ca²⁺ as indicated. Control and test records are from the same channel. Suramin was added to the cis side. A, activation of single channel current by 20 to 100 μM Ca²⁺ and 0.3, 0.6, and 0.9 mM suramin added sequentially to the cis side to give the indicated final concentration. Significantly different (P = 0.05), control vs. 0.3, 0.6, and 0.9 mM suramin; 0.3 mM suramin vs. 0.9 mM suramin (ANOVA). B, activation of single channel current by 1.2 mM suramin at 0.6 μM Ca²⁺ (cis). Control (0.6 μM Ca²⁺) vs. suramin (at 0.6 μM Ca²⁺) was significantly different (P = 0.03; t test). C, activation of single channel current by 1.2 mM suramin and 1.2 mM suramin plus 80 μM 4-CMPS at 0.05 μM Ca²⁺ (cis). Significantly different (P = 0.000001): Control (0.05 μM Ca) vs. suramin or suramin plus 4-CMPS (ANOVA). Values are presented as mean ± S.E.M. for the number of experiments (n).