Alcohol modulation of BK channel gating depends on β subunit composition
| Autor: | Guruprasad Kuntamallappanavar, Alejandro M. Dopico |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
0301 basic medicine
BK channel Physiology Protein subunit Xenopus Allosteric regulation chemistry.chemical_element Gating Calcium 03 medical and health sciences chemistry.chemical_compound Mice Allosteric Regulation Animals Large-Conductance Calcium-Activated Potassium Channel alpha Subunits Research Articles Ethanol biology Chemistry Conductance Coupling (electronics) Protein Subunits 030104 developmental biology Biochemistry biology.protein Biophysics Protein Multimerization Ion Channel Gating Research Article |
| Zdroj: | The Journal of General Physiology |
| ISSN: | 1540-7748 |
| Popis: | Large conductance K+ channels of the slo1 family are gated by Ca2+ and voltage and either inhibited or potentiated by ethanol. Kuntamallappanavar and Dopico analyze the effects of ethanol in detail and find that the absence or presence of β subunits leads to differential modification of channel gating parameters by intoxicating levels of ethanol. In most mammalian tissues, Ca2+i/voltage-gated, large conductance K+ (BK) channels consist of channel-forming slo1 and auxiliary (β1–β4) subunits. When Ca2+i (3–20 µM) reaches the vicinity of BK channels and increases their activity at physiological voltages, β1- and β4-containing BK channels are, respectively, inhibited and potentiated by intoxicating levels of ethanol (50 mM). Previous studies using different slo1s, lipid environments, and Ca2+i concentrations—all determinants of the BK response to ethanol—made it impossible to determine the specific contribution of β subunits to ethanol action on BK activity. Furthermore, these studies measured ethanol action on ionic current under a limited range of stimuli, rendering no information on the gating processes targeted by alcohol and their regulation by βs. Here, we used identical experimental conditions to obtain single-channel and macroscopic currents of the same slo1 channel (“cbv1” from rat cerebral artery myocytes) in the presence and absence of 50 mM ethanol. First, we assessed the role five different β subunits (1,2,2-IR, 3-variant d, and 4) in ethanol action on channel function. Thus, two phenotypes were identified: (1) ethanol potentiated cbv1-, cbv1+β3-, and cbv1+β4-mediated currents at low Ca2+i while inhibiting current at high Ca2+i, the potentiation–inhibition crossover occurring at 20 µM Ca2+i; (2) for cbv1+β1, cbv1+wt β2, and cbv1+β2-IR, this crossover was shifted to ∼3 µM Ca2+i. Second, applying Horrigan–Aldrich gating analysis on both phenotypes, we show that ethanol fails to modify intrinsic gating and the voltage-dependent parameters under examination. For cbv1, however, ethanol (a) drastically increases the channel’s apparent Ca2+ affinity (nine-times decrease in Kd) and (b) very mildly decreases allosteric coupling between Ca2+ binding and channel opening (C). The decreased Kd leads to increased channel activity. For cbv1+β1, ethanol (a) also decreases Kd, yet this decrease (two times) is much smaller than that of cbv1; (b) reduces C; and (c) decreases coupling between Ca2+ binding and voltage sensing (parameter E). Decreased allosteric coupling leads to diminished BK activity. Thus, we have identified critical gating modifications that lead to the differential actions of ethanol on slo1 with and without different β subunits. |
| Databáze: | OpenAIRE |
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