REGIONAL DIFFERENCES IN BIOELECTRICAL PROPERTIES AND ANION SECRETION IN CULTURED EPITHELIA FROM RAT AND HUMAN MALE EXCURRENT DUCTS

Bioelectrical properties and anion secretion in cultured epithelia fro m different regions of rat and human male excurrent ducts were studied by measuring the short-circuit currents (I-SC). In all regions of the rat excurrent duct, Cl- secretion accounts for over 90% of the basal I-SC, although the magnitude varied in different regions. Cl- secretio n was found to be mediated by a Cl-/HCO3- exchanger, an Na+/H+ exchang er, and an Na+/K+/2Cl(-) symport located on the basolateral side of th e epithelial cells. Forskolin, an activator of adenylate cyclase, and ionomycin, a Ca2+ ionophore, were used to investigate the relative imp ortance of cAMP and Ca2+ as intracellular messengers regulating Cl- se cretion in different regions. It was found that in both species, the f orskolin-evoked I-SC response was larger in the proximal end (efferent duct/caput epididymidis [rat/human, respectively]) than in the distal end (cauda/corpus epididymidis). The response to ionomycin in the rat cauda epididymidis (distal end) was larger than that in the efferent duct (proximal end); on the other hand, no significant difference in t he ionomycin-induced I-SC was observed in the caput and the corpus reg ions from the human epididymis. Our results indicate that while the cA MP- and Ca2+-dependent pathways are both involved in regulating Cl- se cretion in all regions along the male excurrent ducts in both species, a regional difference exists with respect to the relative importance of the two regulatory pathways involved in Cl- secretion along the mal e reproductive tract.