Paul De Weer

Na+, K+ EXCHANGE AND Na+, Na+ EXCHANGE IN THE GIANT AXON OF THE SQUID*

In 1960, Caldwell, Hodgkin, Keynes, and Shawl published the remarkable finding that, when a squid axon is exposed to cyanide, active sodium efflux goes on undiminished for some time, whereas the usual2 dependence of active sodium efflux on external potassium ions (KO) disappears within a few minutes. For example, in the absence of extracellular potassium ions, incipient cyanide poisoning (or “partial” poisoning with dinitrophenol) caused an increase in sodium efflux. In addition, there was evidence that the potassium-insensitive sodium efflux required the presence of external sodium (Nao), and the suggestion was made that this KO-independent, Nao-dependent, sodium efflux consisted, in fact, of a sodium-for-sodium exchange across the cell membrane. More recent research by the Cambridge group3 has indeed revealed the existence of a ouabain-sensitive sodium influx of the expected magnitude in partially poisoned squid axons. The purpose of the present communication is to review the factors responsible for the generation of Na:Na exchange across the squid axon membrane, and to compare the electrical effects of this exchange with those of the normal Na:K exchange.

Intracellular pH transients induced by CO2 or NH3

Experiments are reviewed in which intracellular pH (pHi), during exposure of a cell to CO2 -or NHi-containing solutions, not only undergoes an acidification or alkalinization, respectively, but tends to return toward its original value and, upon removal of the test solution, rebounds to a value more alkaline or acid, respectively, than the initial one. A simple physicochemical model is discussed which interprets these observations both qualitatively and quantitatively. In the case of NH3-induced transients, only passive movements seem to take place; in the CO2-induced transients one must postulate an active ‘proton pump’. Experimentally verifiable predictions can be made from these models. It is suggested that many physiological effects following exposure to CO2 or NH3 may be subject to similar transients and rebounds.

Purification, solubility, and pKa of veratridine

The alkaloid neurotoxin veratridine is widely used by cell physiologists to increase membrane sodium permeability. The compound is only sporadically available from commercial sources, but can be purified (Kupchan et al., 1953, J. Amer. Chem. Soc. 75, 5519-5524) from veratrine, a mixture of several alkaloids. We describe here a purification procedure only slightly modified from that of Kupchan et al., and include important details not mentioned in the original paper. Ultraviolet and infrared spectra are presented. We have also determined the pKa and solubility of veratridine in 150 mM NaCl at 25 degrees C. The solubility is steeply pH dependent, ranging from 0.61 +/- 0.02 mM above pH 12 to 18.5 mM at pH 8.07. The pKa, determined from the solubility versus pH curve, was found to be 9.54 +/- 0.02.

Transport adenosine triphosphatase: Absence of ATP: p-Nitrophenol phosphotransferase activity☆

Abstract It is generally accepted that transport adenosine triphosphatase hydrolyzes both ATP and p -nitrophenyl phosphate, and other authors have shown that the enzyme can be phosphorylated in the same location by either substrate. We could detect no label exchange between ATP and p -nitrophenol. This finding indicates that any common phosphorylated intermediate must be formed from either substrate in a poorly reversible reaction and places constraints on models for the sodium pump.