Monovalent cations contribute to T-type calcium channel (Cav3.1 and Cav3.2) selectivity.
Low voltage-activated (LVA) Ca2+ channels regulate chemical signaling by their ability to select for Ca2+. Whereas Ca2+ is the main permeating species through Ca2+ channels, Ca2+ permeation may be modified by abundant intra- and extracellular monovalent cations. Therefore, we explored monovalent cation regulation of LVA Ca2+ permeation in the cloned T-type Ca2+ channels alpha1G (Cav3.1) and alpha1H (Cav3.2). In physiological [Ca2+], the reversal potential in symmetrical Li+ was 19 mV in alpha1G and 18 mV in alpha1H, in symmetrical Cs+ the reversal potential was 36 mV in alpha1G and 37 mV in alpha1H, and in the bi-ionic condition with Li+ in the bath and Cs+ in the pipette, the reversal potential was 46 mV in both alpha1G and alpha1H. When Cs+ was used in the pipette, replacement of external Cs+ with Li+ (or Na+) shifted the reversal potential positive by 5-6 mV and increased the net inward current in alpha1G. Taken together the data indicate that in physiological [Ca2+], external Li+ (or Na+) permeates more readily than external Cs+, resulting in a positive shift of the reversal potential. We conclude that external monovalent cations dictate T-type Ca2+ channel selectivity by permeating through the channel. Similar to Li+, we previously reported that external [H+] can regulate T-type Ca2+ channel selectivity. Alpha1H's selectivity was more sensitive to external pH changes compared to alpha1G. When Cs+ was used in the pipette and Li+ was used in the bath external acidification from pHo 7.4 to 6.0 caused a negative shift of the reversal by 8 mV in alpha1H. Replacement of internal Cs+ with Li+ reduced the pH-induced shift of the reversal potential to 2 mV. We conclude that, similar to other external monovalent cations, H+ can modify T-type Ca2+ channel selectivity. However, in contrast to external monovalent ions that readily permeate, H+ regulate T-type Ca2+ channel selectivity by increasing the relative permeability of the internal monovalent cation.
Delisle
B P
BP
Department of Medicine, The University of Wisconsin, Madison, WI 53706, USA.
Satin
J
J
D001693:Biological Transport, Active / Q000502:physiology; D020747:Calcium Channels, T-Type / Q000737:chemistry / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002412:Cations / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D002586:Cesium / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000502:physiology*; D007668:Kidney / Q000196:embryology / Q000378:metabolism*; D008094:Lithium / Q000737:chemistry / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology*; D012680:Sensitivity and Specificity
C121855:CACNA1G protein, human; C479952:CACNA1H protein, human; D020747:Calcium Channels, T-Type; D002412:Cations; D002586:Cesium; D008094:Lithium