ABSTRACT
The physiological changes which occur during insect moulting are brought about by the steroid hormone 20-hydroxyecdysone (Riddiford & Truman, 1978). The prohormone ecdysone is secreted by the bilaterally paired prothoracic glands (PGs) in response to prothoracicotropic hormone (PTTH) released from the brain (Bollenbacher, Agui, Granger & Gilbert, 1979). Recently, Smith, Gilbert & Bollenbacher (1985) demonstrated that Ca2+ is required for PTTH-stimulated ecdysone synthesis and, consequently, proposed the existence of a hormone-dependent calcium channel associated with the PTTH receptor. In the present study, we show for the first time the existence of voltage-dependent calcium channels in PG cells. Furthermore, we have observed electrical coupling between the cells which appears sufficiently strong to permit the propagation of an action potential throughout the gland in response to stimulation at a single location.
