Changes in cytosolic calcium during cholinergic and adrenergic stimulation of the parotid salivary gland

Abstract

Ca-selective microelectrodes were used to examine calcium transport during acetylcholine (ACh) and Epinephrine (Ep) stimulation of amylase secretion in the parotid gland. The cytosolic concentration of free ionized Ca²⁺ ([Ca]_i) determined in unstimulated cells was 0.44 ±0.04 μM. By measuring the induced changes in intracellular electrode potentials (E_Ca, E_M) we were able to demonstrate that ACh at 10⁻⁹, 10⁻⁸, 10⁻⁷, 10⁻⁶, and 10⁻⁵ M increased [Ca]_i by 0.20±0.02, 0.61±0.04, 0.53±0.02, 0.30±0.05, and 0.14±0.03 μM. Similarly, Ep increased [Ca]_i by 0.14±0.01, 0.42±0.06, 0.31±0.04, 0.15±0.03, and 0.05±0.04, respectively. Removal of extracellular Ca²⁺ significantly (P<0.001) altered the changes in E_Ca in response to ACh and Ep stimulation, thereby demonstrating that the induced increases in [Ca]_i must be due to a transmembrane movement of Ca²⁺. Enzyme secretion was found to vary with the concentration of the stimulus used. Maximal secretion occurred during stimulation using 10⁻⁷ M and 10⁻⁸ M Ep with a suppression of release at supramaximal concentrations. The dose-response curve for ACh differed in that there were two concentrations of stimulus (2×10⁻⁹ and 1×10⁻⁶ M ACh) in which the greatest rate of secretion occurred. Concentrations of stimulus which increase [Ca]_i between 0.86±0.06 μM and 0.74±0.05 appeared to produce optimal amylase secretion, indicating that salivary secretion in the mouse parotid is regulated within a narrow concentration range of cytosolic Ca²⁺.