Heptaminol hydrochloride as an epithelium transporter

Electrophysiological and transport effects induced by heptaminol hydrochloride were studied in frog epithelium. This tissue, which can easily be maintained in vitro, is a valuable model for studying sodium active transport with hormone-dependent characteristics that reproduce mammalian nephron behavior (notably in areas with tight gap junctions). The two following techniques were used: the Ussing short-circuit current method and the swept-frequency impedance measurement method. Our findings indicate the following. (i) Heptaminol hydrochloride significantly increases the short-circuit current and transepithelial polarization. (ii) This effect develops progressively as the molecule is introduced on the serous side (3Na+/2K+ active countertransport sites). Time to maximum development is approximately 20 min and the electrophysiological effect lasts from 60 to 90 min. (iii) The mean equivalent cationic current rise is larger in sulfate-Ringer (+23 +/- 4.6 microA, p less than 0.01) than in chloride-Ringer (+14 +/- 4.9 microA, p less than 0.05). The increase in short-circuit current is approximately 0.9 muequiv. cm-2 h-1 in sulfate-Ringer. (iv) The increase in mean polarization is greater in chloride (+21 +/- 6.2 mV, p less than 0.02) than in sulfate (+6 +/- 1.5 mV, p less than 0.01) following a diphasic effect on potential. (v) Changes in apical impedance Z are small (-454 +/- 323 omega, nonsignificant) compared with transepithelial resistance in sulfate (-1065 +/- 359 omega, p less than 0.05). (vi) Changes in membrane capacitance reflect changes in the membrane surface. However, no significant capacitance changes are produced in sulfate and chloride solution by heptaminol hydrochloride (-0.04 +/- 0.11 microF and 0.05 +/- 0.11 microF, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)