Preliminary measurements of intracellular calcium in an insect salivary gland using a calcium-sensitive microelectrode

Abstract

A calcium-sensitive microeletrode was used to measure free intracellular calcium in salivary gland cells of Calliphora during stimulation with 5-hydroxytryptamine (5-HT). The resting level of calcium was approximately 10 −7M or less but increased in a dose-dependent way sometimes to levels in excess of 10 −6M. The onset of the calcium signal was closely related to changes in membrane and transepithelial potential. This calcium response was greatly reduced when the extracellular calcium concentration was reduced from 10 −3 to 10 −4M. This dependence on external calcium is consistent with previous observations that 5-HT acts to increase the permeability of the basal plasma membrane to calcium. These observations indicate that an increase in the intracellular level of calcium is an early event associated with the onset of fluid secretion in this insect salivary gland.