Relationship between quin2-determined cytosolic [Ca2+] and sweat secretion

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Abstract
Although both methacholine (MCh)- and A23187-induced sweat secretion are known to be strictly dependent on extracellular Ca2+, the role of intracellular calcium concentration ([Ca2+]i) in eccrine sweating has not been clarified. Partially purified eccrine secretory cells were prepared from 400 to 600 isolated secretory coils of monkey sweat glands by serial collagenase digestion and Percoll gradient centrifugation. The quin2 method was used for semiquantitative determination of [Ca2+]i, MCh increased [Ca2+]i in a dose-dependent, reversible, and pharmacologically specific manner (from the resting [Ca2+]i of 80-320 nM) but failed to increase [Ca2+]i in a Ca2+-free medium. A23187 (10(-7) M) increased [Ca2+]i to approximately 900 nM. Theophylline (TH), isoproterenol (ISO), and forskolin (FK) had no effect on the resting [Ca2+]i but, in combination, attenuated the effect of subsequently added MCh and A23187. A23187 at 10(-7) M failed to stimulate sweat secretion or CO2 production in vitro from the quin2-loaded intact isolated sweat glands and dispersed sweat secretory cells, respectively. The observed dissociation between the increase in [Ca2+] may suggest either that MCh stimulation induces some unknown excitatory signal in addition to a rise in [Ca2+] or that A23187-induced Ca2+ influx into the secretory cells is much lower in undissociated sweat glands.