Possible role of Na+‐K+‐ATPase in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide

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Abstract
1 This study was designed to determine the role of sodium-potassium adenosine triphosphatase (Na+-K+-ATPase) in the regulation of human corpus cavernosum smooth muscle contractility by nitric oxide (NO). In addition, we determined if the modulation of Na+-K+-ATPase activity by NO is dependent on the increases in intracellular cyclic GMP concentration. 2 The effect of NO donors, sodium-nitroprusside (SNP) and S-nitroso-glutathione (S-NO-Glu), and a permeable cyclic GMP analogue, 8-bromo-cyclic GMP, on Na+-K+-ATPase activity (measured as ouabain-sensitive 86Rb-uptake) was studied in human cultured corpus cavernosum smooth muscle cells (HCCSMC). In addition, the effect of the cyclic GMP lowering agent, methylene blue, on NO-induced increase in Na+-K+-ATPase activity was studied. 3 SNP (1 μm) caused time-dependent increases in ouabain-sensitive Rb-uptake (33–72%) over 2–20 min in HCCSMC. The stimulation of ouabain-sensitive Rb-uptake by SNP was concentration-dependent (30 and 102% with 0.1 and 1 μm SNP, respectively). Similarly, significant increases in ouabain-sensitive Rb-uptake were obtained with 1 and 10 μm S-NO-Glu. In contrast, incubation of HCCSMC with 8-bromo-cyclic GMP (100 μm) did not increase ouabain-sensitive Rb-uptake. 4 S-NO-Glu induced-increase in intracellular cyclic GMP synthesis, but not the increase in ouabain-sensitive Rb-uptake, was completely inhibited by methylene blue in HCCSMC. 5 The Na+-K+-ATPase inhibitor, ouabain, caused a concentration-dependent increase in tension (0.5 to 2 fold) in tissues contracted with 15 mM KCL. SNP and S-NO-Glu caused a concentration-dependent relaxation (concentration required to cause half maximal relaxation (ED50) = 0.04 and 0.2 μm, respectively) of HCC strips contracted with 15 mM K+. Ouabain (0.1 to 10 μm) inhibited the response to SNP and S-NO-Glu by shifting the concentration-response curves to the right and preventing full smooth muscle relaxation. 6 These results indicate that the activity of Na+-K+-ATPase modulates the contractility of HCC smooth muscle, and that NO stimulates Na+-K+-ATPase activity in HCCSMC independently of its ability to increase the intracellular cyclic GMP concentration. They also suggest that stimulation of Na+-K+-ATPase activity plays an important role in NO-induced relaxation of HCC smooth muscle