Voltage-gated calcium currents in whole-cell patch-clamped bullfrog dorsal root ganglion cells: effects of cell size and intracellular solutions.
Acutely dissociated bullfrog dorsal root ganglion (DRG) cells could be divided into two classes by measurement of cell capacitance. A bimodal distribution of cell capacitance was found and a value of 75 pF was used to divide frog DRG cells into 'small' and 'large' types. Two distinct voltage-activated Ca2+ currents were evoked in both classes of cells: a rapidly inactivating, low-voltage-activated current and a slowly-inactivating, high-voltage-activated current. When the recording pipette contained CsCl, greater peak inward current values and densities were seen in large cells compared to small cells. No significant differences were observed in the distribution of low-and high-voltage-activated currents in small and large cells. Replacement of pipette solutions containing CsCl with solutions containing equimolar concentrations of Cs glutamate, L-arginine Cl, or N-methyl-D-glucamine significantly increased both the reversal potential and the maximum amplitude of the Ca2+ currents in both small and large DRG cells. These increases indicate that internal substitutions with organic ions suppresses outward currents more effectively than does CsCl. In contrast to findings with CsCl, when organic ions were used in the pipette solution a significantly higher proportion of low-threshold Ca2+ channels was observed in small cells compared to large cells. These observations indicate that when organic solutions were used internally, significant differences in the proportion of low-threshold to high-threshold Ca2+ channels were observed in small and large cells. The composition of the internal solution is a critical variable when determining the type and amount of inward Ca2+ current in different types of neurons.
Holohean
A M
AM
Neurophysiology Laboratory, Veteran's Administration Medical Center, Miami, FL, USA.
Rodriguez
C A
CA
Hackman
J C
JC
Davidoff
R A
RA
D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D048429:Cell Size / Q000502:physiology*; D005727:Ganglia, Spinal / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana; D013997:Time Factors
D015220:Calcium Channels