The guinea-pig seminal vesicle in vivo is characterized by a transmural electrical potential difference of approximately 11 mV with the lumen electrically negative with respect to the interstitial fluid. The concentrations of Na, Cl and K in the vesicular fluid are 13, 15, and 0-4 mM, respectively. 2. When mounted as a flat sheet in a short-circuit apparatus, guinea-pig seminal vesicles initially undergo a decline in the transmural electrical potential difference and short-circuit current ('low phase') followed by a spontaneous increase in these parameters ('high phase'). 3. During the low phase, net C1 movements across the tissue do not differ significantly from zero, and there is a small 'residual' current that is unaccounted for. 4. During the high phase, there is a significant active C1 secretion into the mucosal solution, not detectable net movement of Na and an unaccounted for or 'residual' current that is equal to that found in the low phase. 5. Theophylline, dibutyryl-3'-5' cyclic adenosinemonophosphate,prostaglandin E1 and prostaglandin F2alpha markedly stimulate the transmural electrical potential difference and short-circuit current during the low phase, but have no effect when added to the bathing solution during the high phase. 6. Diffusion potentials determined across in vitro seminal vesicles suggest that the spontaneous transmural electrical potential difference in vivo may be attributable to the large ionic asymmetries between the vesicular fluid and the plasma. 7. It is postulated that two phases are involved in the elaboration of seminal vesicular fluid. The initial phase, following emptying of the vesicle, is characterized by the secretion of electrolytes, organic molecules and water. Active C1 secretion presumably regulated by intracellular cyclic adenosinemonophosphate and/or prostaglandins may be the driving force for this initial secretion of electrolytes. Following this secretory phase, electrolytes and water are reabsorbed, thereby concentrating the organic components in the vesicular reservoir.
