Effects of manganese and other agents on the calcium uptake that follows depolarization of squid axons.
1. The Ca-sensitive photoprotein aequorin was injected into squid axons and the light response to stimulation or depolarizing voltage clamp pulses recorded.2. The effects of Mn(2+), Co(2+), Ni(2+), La(3+) and of the organic Ca antagonists D-600 and iproveratril on the early tetrodotoxin-sensitive and late tetrodotoxin-insensitive components of the light response were studied.3. The late tetrodotoxin-insensitive component can be blocked, reversibly, by concentrations of Mn, Co and Ni that reduce but do not block the tetrodotoxin-sensitive component. The late component can also be blocked by La(3+) and the organic Ca antagonists D-600 and iproveratril.4. Mn(2+), Co(2+), Ni(2+) and the drug D-600 all reduce the Na currents, but have little effect on either outward or inward K currents. Tetraethylammonium blocks the outward K current but has no appreciable effect on the tetrodotoxin-insensitive entry of Ca.5. Concentrations of Mn between 5 and 50 mM substantially reduce the light output during a train of action potentials; they also slightly reduce the rate of rise of the action potential.6. On pharmacological grounds it is concluded that the tetrodotoxin-insensitive component of Ca entry does not represent Ca ions passing through the K permeability channels. There must exist a potential-dependent late Ca channel that is distinct from the well known Na and K channels of the action potential. A possible function for this late Ca channel in the coupling of excitation to secretion is discussed.
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003035:Cobalt / Q000494:pharmacology; D049832:Decapodiformes; D004558:Electric Stimulation; D007811:Lanthanum / Q000494:pharmacology; D008163:Luminescent Measurements; D008345:Manganese / Q000494:pharmacology*; D008738:Methyl Ethers / Q000494:pharmacology; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D010777:Photochemistry; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D008738:Methyl Ethers; D009467:Neuromuscular Depolarizing Agents; D003035:Cobalt; D008345:Manganese; D013779:Tetrodotoxin; D007811:Lanthanum; D009532:Nickel; D012964:Sodium; D014700:Verapamil; D011188:Potassium; D002118:Calcium