A simple method for embedding small specimens for photomicrography and sectioning following intracellular microiontophoresis of lucifer yellow CH

Electrophysiological and dye-coupling studies on secretory, myoepithelial and duct cells in human eccrine sweat glands

1. Electrophysiological properties and dye-coupling status of secretory, myoepithelial and coiled duct cells in isolated human eccrine sweat glands have been assessed by single-micro-electrode studies and intracellular micro-iontophoresis of the fluorescent naphthalimide dye Lucifer Yellow CH (molecular weight 457). Treated glands were embedded in LKB HistoResin and examined by transmission fluorescence microscopy, first as wholemounts and then as 5 microns serial sections. Sections positive for Lucifer Yellow were photographed and then stained with Toluidine Blue for observation by conventional microscopy to confirm the site of penetration. 2. Out of forty-five successful micro-iontophoreses, three were confirmed in secretory cells, twelve in myoepithelial cells and thirty in cells of the coiled duct wall. The latter were identified as the most penetrable in the coiled part of the isolated human eccrine sweat gland. 3. Of the three secretory cells labelled (resting potentials -40, -52 and -63 mV), all demonstrated dye coupling to neighbouring secretory cells although in one case this was found to be selective. Not every secretory cell was involved in coupling. No fluorescent label spread to the myoepithelial cells which form a network on the basal surface of the secretory tubule. 4. When myoepithelial cells were penetrated, they demonstrated dye coupling to neighbouring myoepithelial cells but not to secretory cells with which they also made contact. Basal resting potentials of -35 to -65 mV were recorded (mean = -52 mV, S.E. of mean = +/- 2.4 mV, n = 12) and, in eight out of the twelve cells penetrated and labelled, spontaneous depolarizing transients were also observed whose amplitude but not frequency increased with increasing membrane polarization. Administration of acetylcholine to produce a final concentration of 10(-6) to 10(-7) M produced either depolarization or micro-electrode dislodgement. 5. Of the thirty cells labelled in the coiled duct, twenty-six showed obvious dye spread to neighbouring cells in both layers of the wall. There was no relation between dye-coupling status and basal resting potential which lay in the range -40 to -82 mV (mean = -60 mV, S.E. of mean = +/- 2.4 mV, n = 30). Repeated doses of acetylcholine produced either no response from cells in this range or depolarization in cells with resting potentials more negative than -70 mV and hyperpolarization in cells with resting potentials more positive than -70 mV. In addition, there was a biphasic response, depolarization followed by hyperpolarization in a cell of resting potential -67 mV.(ABSTRACT TRUNCATED AT 400 WORDS)