Nitric oxide activation of a potassium channel (BKCa) in feline lower esophageal sphincter

Figure 1 Representative traces (last 300 ms of trace shown) and quantification of the effect of sodium nitroprusside (10^-4 mol/L) on elicited outward K⁺ currents using a ramp protocol from -140 to +60 mV of lower esophageal sphincter circular (n = 13) and sling (n = 8) smooth muscle cells. The maximal total outward current was similar in isolated smooth muscle cells from the lower esophageal sphincter (LES) circular and sling regions. The nitric oxide donor sodium nitroprusside (SNP) increased outward potassium currents of LES circular smooth muscle cells. In contrast, SNP did not significantly cause an increase in the outward K⁺ currents in LES sling muscle. ^bP < 0.001.

Figure 2 Pharmacological identification, with iberiotoxin (200 nmol/L), of the portion of the elicited outward K⁺ currents, using a ramp protocol from -140 to +60 mV, corresponding to BK_Ca channel currents in lower esophageal sphincter circular (n = 8) smooth muscle cells. Last 300 ms of representative traces shown. Sodium nitroprusside (SNP) induced a significant increase in elicited outward potassium currents vs control current density. Iberiotoxin (IbTX) alone blocked a significant portion of the control outward potassium currents. SNP added in the presence of IbTX, produced no significant increase in the outward currents. ^aP < 0.05.

Figure 3 Representative traces and quantification of the effect of L-NNA (10^-4 mol/L) on elicited outward K⁺ currents using a ramp protocol from -70 to +70 mV of lower esophageal sphincter circular (n = 8) and sling (n = 8) smooth muscle cells. Addition of L-NNA led to an insignificant 14% decrease in outward potassium currents in the circular smooth muscle cells. In the sling smooth muscle cells, the addition of L-NNA led to an insignificant 7% reduction in current density.

Figure 4 Effect of the blockade of the BK_Ca channel with iberiotoxin (10^-7 mol/L) of lower esophageal sphincter (A) circular (n = 6-8) and (B) sling (n = 7-11) smooth muscle tone with intact nerves or blocked with tetrodotoxin (10^-6 mol/L). A: For the circular muscle, tetrodotoxin (TTX) or iberiotoxin (IbTX) did not significantly change the resting tension (P > 0.05). The combined blockade of the nerves and the BK_Ca channel also resulted in no significant change of the overall muscle tone (P > 0.05); B: Similarly, for the sling muscle, TTX, IbTX or TTX and IbTX together did not significantly modulate the basal resting tone (P > 0.05). //: Separates different experiments.

Figure 5 Effect of sodium nitroprusside (10^-4 mol/L) ± iberiotoxin (10^-7 mol/L), and iberiotoxin (10^-7 mol/L) ± sodium nitroprusside (10^-4 mol/L) on smooth muscle tone relative to basal tone in the presence of tetrodotoxin (10^-6 mol/L) in muscle strips of lower esophageal sphincter (A) circular (n = 6) and (B) sling (n = 6-9) muscles. A: In lower esophageal sphincter (LES) circular muscle, sodium nitroprusside (SNP) decreased the resting tension and this tension was then unchanged with further addition of iberiotoxin (IbTX) (P > 0.05). When IbTX was added first, there was no significant change in tension, while the subsequent addition of SNP [IbTX+SNP in the presence of tetrodotoxin (TTX)] significantly decreased the tension (P < 0.001); B: In LES sling muscle, SNP or SNP+IbTX decreased the tension to the same extent, and IbTX alone produced no significant change in resting tension. IbTX+SNP decreased the tension (P < 0.001). //: Separates different experiments. ^bP < 0.001.