Secretion of a potassium-rich fluid by the secretory coil of the rat paw eccrine sweat gland.

1. It is already known that the rat paw eccrine sweat contains high K(+) (greater than 150 mM) and low Na(+) concentrations (less than 70 mM). The present study was intended to clarify the site of K(+) secretion within the sweat gland, namely, the duct or the secretory coil. In vivo paw sweat was first induced by systemic pilocarpine injection or nerve stimulation. Both K(+) and Na(+) concentrations were studied in relation to the sweat rate to determine indirectly whether there is ductal secretion or reabsorption.2. Both Na(+) and K(+) concentrations in paw sweat agreed with the previous studies but did not show any saturation-type flow dependence at the high sweat rate range.3. A method has been developed to isolate a single segment of the secretory coil and induce sweat secretion directly from it in an in vitro condition.4. In the presence of fresh serum (30%, preincubated for 30 min at 56 degrees C) in the incubation medium, stable secretory activity due to 10(-6)M-Mecholyl could be maintained for 40 min or longer. The primary sweat thus induced contained low Na(+) (30 mM) and high K(+) (160 mM) concentrations.5. In the secretory coil sweat in vitro, K(+) concentration decreased and Na(+) concentration increased as the secretory rate fell either spontaneously or after addition of atropine or cyanide.6. It remains to be studied whether auxiliary ductal secretion or reabsorption is present at low rates of sweating in the rat sweat gland.7. It was concluded that the secretory coil of the rat paw sweat gland is the major, if not the sole, site of K(+) secretion.