Bell-shaped calcium-response curves of Ins(1,4,5)P3- and calcium-gated channels from endoplasmic reticulum of cerebellum.
Release of calcium from intracellular stores occurs by two pathways, an inositol 1,4,5-trisphosphate (InsP3)-gated channel and a calcium-gated channel (ryanodine receptor). Using specific antibodies, both receptors were found in Purkinje cells of cerebellum. We have now compared the functional properties of the channels corresponding to the two receptors by incorporating endoplasmic reticulum vesicles from canine cerebellum into planar bilayers. InsP3-gated channels were observed most frequently. Another channel type was activated by adenine nucleotides or caffeine, inhibited by ruthenium red, and modified by ryanodine, characteristics of the ryanodine receptor/channel6. The open probability of both channel types displayed a bell-shaped curve for dependence on calcium. For the InsP3-gated channel, the maximum probability of opening occurred at 0.2 microM free calcium, with sharp decreases on either side of the maximum. Maximum activity for the ryanodine receptor/channel was maintained between 1 and 100 microM calcium. Thus, within the physiological range of cytoplasmic calcium, the InsP3-gated channel itself allows positive feedback and then negative feedback for calcium release, whereas the ryanodine receptor/channel behaves solely as a calcium-activated channel. The existence in the same cell of two channels with different responses to calcium and different ligand sensitivities provides a basis for complex patterns of intracellular calcium regulation.
Bezprozvanny
I
I
Department of Medicine, University of Connecticut, Health Center, Farmington 06032.
Watras
J
J
Ehrlich
B E
BE
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002531:Cerebellum / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005246:Feedback; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015640:Ion Channel Gating / Q000187:drug effects*; D008051:Lipid Bilayers / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000502:physiology; D011950:Receptors, Cholinergic / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008051:Lipid Bilayers; D011956:Receptors, Cell Surface; D011950:Receptors, Cholinergic; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium