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 from 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- secretion was found to be mediated by a Cl-/HCO3- exchanger, an Na+/H+ exchanger, and an Na+/K+/2Cl(-) symport located on the basolateral side of the epithelial cells. Forskolin, an activator of adenylate cyclase, and ionomycin, a Ca2+ ionophore, were used to investigate the relative importance of cAMP and Ca2+ as intracellular messengers regulating Cl- secretion in different regions. It was found that in both species, the forskolin-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 the ionomycin-induced I-SC was observed in the caput and the corpus regions from the human epididymis. Our results indicate that while the cAMP- and Ca2+-dependent pathways are both involved in regulating Cl- secretion 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 male reproductive tract.