A temperature control system for small biological preparations, displaying relatively fast heating and cooling capability

Effect of amiloride on electrolyte transport parameters of the main duct of the rabbit mandibular salivary gland

We have studied the response of the rabbit mandibular main duct perfused in vitro to luminally administered amiloride. The half-maximal inhibitory concentrations (KI) when the duct was bathed in Cl solutions were: for net Na+ transport, 3 X 10(-6) mol l-1; for transepithelial potential difference, 6 X 10(-6) mol l-1; and for transepithelial conductance, 3 X 10(-7) mol l-1. Substitution of the impermeant SO2-(4) anion for Cl- changed the KI for conductance to 3 X 10(-6) mol l-1. Within Cl- -containing media, the time course of the amiloride effect on potential difference showed an early rapid fall of 10 mV with a half-time 2 s, followed by a slower depolarization of 9 mV, and the conductance change followed the slower component of the potential change. In SO2-(4)-containing media, the potential difference and conductance changes followed time courses similar to one another. Finally, experiments on the effect of serosal applications of ouabain revealed that, although, in general, ouabain reduced resistance, it caused an increase in resistance in those ducts where the initial resistance was low. We conclude that: i) luminal Na+ transport occurs via amiloride-sensitive, conductive Na+ channels; ii) the Cl- conductance is the major determinant of transepithelial conductance; iii) the first phase of the potential response is due to blocking of the Na+ conductive channels, whilst the slow phase reflects secondary inhibition of an electrogenic Na+ pump; and iv) duct resistance changes are secondary to alterations in intracellular Cl- concentration.

Electrical resistance of rabbit submaxillary main duct: a tight epithelium with leaky cell membranes

The electrical resistance of rabbit salivary main duct epithelium has been measured. A small axial electrode, which passed current and measured potential simultaneously, was placed inside the ductal lumen. A cylindrical spiral was wound around the main duct and served as outside current electrode. The instantaneous current voltage relations were linearly up to current densities of 1.5 mA/cm2, independently of the Cl concentration in the bathing solutions. Strong polarization effects were observed in low Cl solutions. There was a significant inverse correlation between the spontaneous potential difference across the epithelium and the epithelial resistance in solutions with either high or low Cl concentrations. In high Cl solutions the epithelial resistance was 12.2 + 1.8 (n = 7) omegacm2. The resistance increased when the mucosal Na and Cl concentrations decreased. After addition of ouabain the resistance always decreased. The temperature dependence of the resistance was determined, and apparent activation energies were calculated. Values for activation energies ranged from 3.2 to 6.5 kcal/mol, depending on the ionic composition of the bathing solutions. Addition of amiloride to the mucosal solution led to an increase in resistance by a factor of 2.1 in high Cl solutions and of 4.1 in low Cl solutions. When ouabain was applied before amiloride, there was no effect on the resistance in high Cl solutions and a smaller increase in the resistance in low Cl solutions. The results of this study support the conclusion that the low resistance of main duct epithelium resides in the cell membranes and is not due to a paracellular pathway.