Leukocytes from Hv1 knockout mice lack voltage-gated proton currents, indicating that Hv1 is essential for these currents in the mouse [12] [14].
However, this mechanism is unlikely in type II pneumocytes, because they lack voltage-gated Ca2+ currents, in resting state as well as during all stages of exocytosis [14].
A recent study showed that AS Na+ channels were expressed in type I taste cells, which lack voltage-gated inward currents [52].
TRPM5 cells, referred to as type II cells, lack voltage-gated calcium channels [41], [42] and release ATP neurotransmitter by a non-conventional pathway involving pannexin/connexin hemichannels gated by voltage [43] [45].
However, a recent study claimed that human parathyroid cells lack voltage-gated Ca2+ channels, and that TRPC ion channels associated with Orai1 and STIM1 may increase intracellular Ca2+ concentration in the cells [23].
Nonspiking interneurons (NSIs), almost exclusively characteristic to arthropod central nervous systems, do not generate action potentials and hence lack voltage-regulated sodium channels, yet having a variety of voltage-regulated potassium conductances on their dendritic membrane including the one similar to the delayed-rectifier type potassium conductance.
Do the T1R3-expressing Type II cells also lack voltage-gated Ca2+ channels?
Although endothelial cells commonly lack voltage-gated Ca2+ channels, some reports do suggest the functional presence of these channels in endothelial cells.
Recent electrophysiological studies suggest that the bitter-sensitive, α-gustducin-expressing subset of Type II cells lack voltage-gated Ca2+ channels and have only small voltage-gated Na+ and K+ currents [ 16].
In 2006 we reported in BMC Biology that Type II cells lack voltage-gated Ca2+ channels and the presynaptic protein SNAP-25-elements normally required for conventional vesicular-mediated synaptic transmission [ 2].
