ABSTRACT
CaCCs are present in ancient life forms such as green algae, where they are involved in action potential generation in the genera Chara and Nitella (Fromm and Lautner, 2007; Shiina and Tazawa, 1987). Highly evolved and complex systems also express these channels. Amphibian physiology is a prominent example, having provided many of the early descriptions of CaCCs. Endogenous CaCCs were observed in Xenopus laevis (Miledi and Parker, 1984) and Rana pipiens oocytes (Cross, 1981), where they prevent polyspermy by activating upon
postfertilization intracellular calcium release, depolarizing the oocyte to block additional sperm entry. Sensory tissues like salamander retina photoreceptors (Bader et al., 1982) and frog olfactory cilia (Kleene and Gesteland, 1991) have also been reported to express CaCCs.
