Rapid activation of calcium-sensitive Na+/H+ exchange induced by 20-hydroxyecdysone in salivary gland cells of Drosophila melanogaster.
Ecdysteroids play an important role in the larval moulting process of insects. 20-Hydroxyecdysone (20E) causes the induction of specific 'puffs' in polytene chromosomes of Drosophila melanogaster salivary gland cells. Although it is known that inorganic ions control pretranscriptional processes in the cell nucleus, the intracellular mechanisms of gene activation are still unclear. Therefore, we examined the effects of 20E on plasma membrane ion transport of Drosophila melanogaster salivary gland cells. Isolated glands of the third larval stage were superfused with a solution mimicking the haemolymph. The relative K+ conductance of the cell membrane (tK+) was measured with microelectrodes by performing ion substitution experiments. Under control conditions tK+ averaged to 0.16 + 0.02 (n = 15). Addition of 5 x 10(-6) M 20E increased tK+ within 2 min by 19.1 +/- 4.2% (n = 15). This rapid response to 20E was elicited only in the presence of calcium. Moreover, starting from a steady-state intracellular pH of 7.20-7.60, 20E induced a rise in cytoplasmic pH by 0.27 +/- 0.06 (n = 6) within minutes. Amiloride (10(-3) M), a blocker of plasma membrane Na+/H+ exchange, prevented the 20E-induced intracellular alkalinization. We conclude that 20E activates a calcium-sensitive plasma membrane Na+/H+ exchange leading to a rise of plasma membrane K+ conductance and intracellular alkalinization both being prerequisites for steroid hormone induced gene activation.
Schneider
S
S
Department of Physiology, University of Würzburg, Germany.
Wünsch
S
S
Schwab
A
A
Oberleithner
H
H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004331:Drosophila melanogaster / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D004441:Ecdysterone / Q000494:pharmacology* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects; D007814:Larva / Q000378:metabolism; D008564:Membrane Potentials; D011522:Protons; D012469:Salivary Glands / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D004441:Ecdysterone; D000584:Amiloride; D012964:Sodium; D002118:Calcium