Table 4.

Roles of Ca²⁺ and calmodulin in mediating the stimulatory effects of PKG activation on normalized single-channel open and closed properties of recombinant Kir6.2/SUR1 channels in intact HEK293 cells

Properties	Zaprinast	+BAPTA-AM	+SKF-7171A
Open probability	4.46 ± 0.42†	1.51 ± 0.33	1.08 ± 0.21
Opening frequency	3.92 ± 0.33‡	1.28 ± 0.26	0.97 ± 0.16
Mean open duration	1.25 ± 0.08*	1.24 ± 0.21	1.05 ± 0.10
Mean closed duration	0.26 ± 0.02§	1.00 ± 0.27	1.65 ± 0.68
Number of patches	5	6	8

Single-channel recordings of Kir6.2/SUR1 and Kir6.2FL4A channels in HEK293 cells and Kir6.2/SUR1 channels in SH-SY5Y cells in cell-attached patches were performed at −60 mV in symmetrical 140 mM K⁺ solutions. Bath application of zaprinast (50 μM) alone or coappliation of zaprinast together with the Ca²⁺ chelator BAPTA-AM (50 μM) or the irreversible calmodulin antagonist SKF-7171A (10 μM) was administered using a pressure-driven perfusion system. Single-channel properties were obtained as described in materials and methods. All values were normalized as described in Table 1 (control taken as 1) and averaged. Data are means ± SE.

^* P < 0.05;

^† P < 0.01;

^‡ P < 0.001;

^§ P < 0.0001 (two-tailed, one-sample t-tests).