Table 3

Effect of magnesium on the suramin-induced activation of the purified calcium release channel.

		P_o	n
A	Control (50 μM Ca²⁺)	0.48 ± 0.06	7
	0.9 mM Suramin	0.84 ± 0.03	7
	4 mM Mg²⁺	0.064 ± 0.020	7
	10 mM Mg²⁺	0.019 ± 0.004	5
B	Control (50 μM Ca²⁺)	0.56 ± 0.04	6
	0.9 mM Suramin	0.87 ± 0.02	6
	1 mM Mg²⁺	0.40 ± 0.07	6
	2.4 mM Suramin	0.68 ± 0.09	4
	4 mM Mg²⁺	0.15 ± 0.05	4
	10 mM Mg²⁺	0.017 ± 0.009	2
C	Control (50–100 μM Ca²⁺)	0.56 ± 0.05	5
	2 mM Mg²⁺	0.045 ± 0.010	5
	0.9 mM Suramin	0.18 ± 0.08	5
	1.5 mM Suramin	0.33 ± 0.02	3

Single-channel currents were recorded at ⁺20 mV holding potential with 480 mM/50 mM CsCl (cis/trans) in the presence of 50 to 100 μM Ca²⁺ (cis). Control and test records are from the same channel. Suramin or magnesium was added sequentially to the cis bath to give the indicated final concentrations. A, activation of single purified calcium release channel by 0.9 mM suramin and inhibition by 4 mM and 10 mM Mg²⁺. Significantly different (P = 0.05): 0.9 mM suramin vs. 0.9 mM suramin plus 4 mM Mg²⁺ or 10 mM Mg²⁺; 0.9 mM suramin plus 4 mM Mg²⁺ vs. 0.9 mM suramin plus 10 mM Mg²⁺ (ANOVA). B, activation of a single purified calcium release channel by 0.9 mM suramin, inhibition by 1 mM Mg²⁺, reactivation by 2.4 mM suramin followed by inhibition with 4 and 10 mM Mg²⁺. C, inhibition of a single calcium release channel by 2 mM Mg²⁺ and reactivation by 0.9 to 1.5 mM suramin. Significantly different (P = 0.05): 2 mM Mg²⁺ vs. 2 mM Mg²⁺plus 1.5 mM suramin (ANOVA). Values are presented as means ± S.E.M. for the number of experiments (n).