COMPARATIVE-STUDIES ON INTRACELLULAR CALCIUM AND NADH FLUORESCENCE OFTHE RABBIT CORPUS CAVERNOSUM

Erectile function (erection and detumescence) involves the complex int eraction of direct neuronal stimulation of corporal smooth muscle, neu rohumoral release of specific endothelial contractile and relaxant fac tors, and secondary modulation by a variety of putative neuropeptides and vasoactive modulators. Using surface spectrofluorometry, we have c orrelated spontaneous contractile activity and the contractile respons e to field and pharmacological agents with intracellular calcium and N ADH metabolism. The results demonstrate that the corpus cavernosal tis sue has very unusual properties. Spontaneous contractile activity is c orrelated with a phasic increase in intracellular calcium. However, sp ontaneous contractile activity is most often correlated with a bi-phas ic effect on the ratio of NADH/NAD. At the start of the spontaneous co ntraction, there is a sharp phasic increase in NADH/NAD; peak contract ile force occurs simultaneous with a phasic decrease in this ratio sho wing that at peak force generation, there is a decrease in the level o f intracellular energy. Phenylephrine stimulation results in an increa se in intracellular calcium in proportion to the increase in tension; however, phenylephrine stimulation at low concentrations results in a net increase in the NADH/NAD ratio whereas high concentrations of phen ylephrine result in a net decrease in the NADH/NAD ratio. In general, field stimulation results in a decrease in tension at low frequencies, a biphasic response at mid-frequencies, and a contraction at high fre quencies. These contractile responses are directly related to alterati ons in the intracellular concentration of calcium. That is, a decrease in tension is preceded by a decrease in intracellular calcium while a n increase in tension is preceded by an increase in intracellular free calcium. Field stimulation results in a rapid and phasic alteration i n the NADH/NAD ratio; however, the NADH/NAD response can be either an increase, decrease, or biphasic response. There does not appear to be a consistent relationship between the contractile/relaxant response to field stimulation and altered NADH/NAD ratio. Finally, ATP, bediarech ol, and nitroprusside induce a decrease in the basal tension of the co rpus cavernosal strips which corresponds with a decrease in the NADH/N AD ratio. However, whereas nitroprusside relaxation is correlated with a decreased intracellular calcium level, both ATP and bethanechol sti mulate an increase in intracellular free calcium. These studies indica te that the response of the corpus cavernosal tissue to both field sti mulation and pharmacological agents is complex and may involve both di rect and indirect actions of a variety of cellular mediators on the co rporal smooth muscle. (C) 1994 Wiley-Liss, Inc.