Voltage-operated cation channels

There are several major classes of Ca channels (1) receptor-operated Ca channels in plasma membranes (2) ligand-gated Ca " channels in intracellular membranes and (3) voltage-dependent Ca channels that are usually found in plasma membranes or the invaginations of the plasma membrane that are known as transverse tubule membranes. Receptor-dependent or receptor-operated Ca channels (ROCCs) are primarily opened in response to activation of their associated receptors and, by definition, exhibit a certain amount of selectivity for Ca " over other cations. Several potentially different types of ROCCs have been characterized including ATP-sensitive channels in smooth muscle [1], mitogen and IP3-sensitive... 

The methods of solute transfer across the serosal/basolateral membrane can include ion channels and antiporters similar to those described earlier. In the case of serosally located cation channels, these primarily work because the intracellular electrolyte concentration is high enough to overcome the electrical gradient (e.g. some K+ channels). For anion channels, the negative charge inside the cell compared with the blood will help drive (repel) anions from the cell (e.g. CL efflux on voltage-sensitive channels in the intestine [58]). In the case of antiporters, the operation is fundamentally the same as that used in the mucosal membrane, except that the driving force is derived from an ion... 

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