Progress in microelectrode techniques for kidney tubules.

Altlhoughi microelectrocle measurements lhave caused a good deal of confusion in the investigation of renal electrolyte transport (for literature see Ref. 4), we cannot do witlhout them. Knowledge of the electrical potential steps, whiclh the ions have to pass (luring their reabsorption, is indispensable for understanding the transport meclhanisms involved. Hence the development of more reliable methods to measure the electrical properties of kidney tubules was an important as well as clhallenging problem. This paper deals witlh some of the advances effected in our laboratory in the past 5 years. The properties of microelectrocles that present the major problems are: 1. the invisil)ility of the electrode tip, 2. the instability of the tip potential, and 3. tlle instability of the tip resistance. Since a brief description of resistance measurement problems lhas been published elsewhere recently(14), only the first two points will be discussed lhere. Simple microscopic observation alone can never tell whetlher the invisible microelectrode tip lhas penetrated the invisible cell membrane. In order to decide whletlher the tip sticks witlhin a cell or wlhetlher it lhas reaclhed the tubular lumen a number of localization metlhods lhave been developed.