Modulation of type A K+ current in Drosophila larval muscle by internal Ca2+; effects of the overexpression of frequenin.
The calcium-dependent modulation of type A K+ current (IA) has been investigated using a two-electrode voltage clamp on larval muscle cells of Drosophila. It was found that the amplitude of IA increases when [Ca2+]o is changed from 0.2 mM to 2 mM. The increase in IA amplitude is not due to overlap with the Ca(2+)-dependent fast K+ current, ICF, since it is observed also in slo1 mutants, which are deficient for this current. This effect is not due to Ca(2+)-dependent shifts in the steady-state activation/inactivation kinetics. The phenomenon is probably due to elevations in internal calcium since it is abolished by Ca2+ channel blockers and promoted by caffeine (5 mM) if added in the absence of external calcium. This calcium effect was dose-dependent since it was not observed in the presence caffeine plus 2 mM calcium in the bath nor for values of [Ca2+]o above 4 mM. The Ca(2+)-dependent modulation of IA is absent in V7, a mutation that causes overexpression of frequenin, a recoverin-like Ca(2+)-binding protein which stimulates guanylyl cyclase [31]. One possible explanation for the loss of IA modulation in the V7 mutation is that the excess of frequenin alters intracellular cGMP-dependent metabolic pathways responsible for the internal calcium homeostasis.
Poulain
C
C
Unité de Physiologie Neuromusculaire, Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS, Gif-sur-Yvette, France.
Ferrús
A
A
Mallart
A
A
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics; D004553:Electric Conductivity; D006706:Homeostasis; D007700:Kinetics; D007814:Larva; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*
D002135:Calcium-Binding Proteins; D029721:Drosophila Proteins; C082454:Frq protein, Drosophila; D009419:Nerve Tissue Proteins; D011188:Potassium; D002118:Calcium