Developmental changes in calcium conductances contribute to the physiological maturation of cerebellar Purkinje neurons in culture

Abstract

The relationship between calcium conductances and developmental changes in the active and passive membrane properties of cerebellar Purkinje neurons from rats was studied in a culture model system by using current-clamp and voltage-clamp techniques. These cultures, at 6–21 d of age, represented the main period of morphological and physiological development of the Purkinje neuron. In the current-clamp studies, input resistance decreased and the current-voltage curve became more S-shaped as the neurons matured in culture. Spike-generating properties also changed. Immature Purkinje neurons without dendritic structure produced repetitive, fast TTX-sensitive simple spikes when stimulated electrically. The simple spike frequency increased with maturation. In older neurons (greater than or equal to 12 d in vitro) with well- developed dendritic structure, a burst event, the complex spike, preceded the repetitive simple spike firing. Magnesium (10 mM) and cadmium (50–100 microM), calcium channel blockers, antagonized the repetitive simple spike firing in both young and old neurons. The complex spike of the older neurons was also antagonized by magnesium (10 mM) but was resistant to cadmium (50–100 microM), suggesting that a pharmacologically distinct calcium conductance mediated this spike event. Whole-cell voltage-clamp recordings showed that the older Purkinje neurons expressed two calcium currents, a low-threshold rapidly inactivating calcium current resistant to cadmium (50–100 microM) and a high-threshold slowly inactivating calcium current antagonized by cadmium (50–100 microM). In young Purkinje neurons without dendritic structure (6–9 d in vitro), only the high-threshold calcium current was evident. The amplitude of this current increased approximately 50% during development. These results indicate that the developmental expression of calcium conductances plays a prominent role in the physiological maturation of the cultured Purkinje neurons, which closely simulate the physiologic cells they model. The high-threshold calcium conductance is expressed early in development and contributes to repetitive simple spike firing of both the young and old neurons. The low-threshold calcium conductance appears later in development, coincident with dendritic expression, and plays a major role in the generation of the complex spike.

Developmental Changes in Calcium Current Pharmacology and Somatostatin Inhibition in Chick Parasympathetic Neurons

“…Developmental changes in Ca 2ϩ current in neurons have been reported previously, but, in general, these reports have been limited either to changes in the magnitude of Ca 2ϩ current expression during development (Dourado and Dryer, 1992;Desarmenien et ., 1993) or to changes in the relative expression of low-voltage and high-voltage-activated current types (Yaari et al, 1987;Gottman et al, 1988;Kostyuk, 1989;McCobb et al, 1989;Thompson and Wong, 1991;Gruol et al, 1992;Mynlieff and Beam, 1992;Rothe and Grantyn, 1994;Lorenzon and Foehring, 1995). In contrast, we report the expression in embryonic neurons of a mixed pharmacologic type of high-voltage-activated current that is replaced by high-voltage-activated current types that are blocked selectively by -CgTX GVIA or dihydropyridine antagonists.…”

Calcium Channel Density and Hippocampal Cell Death with Age in Long-Term Culture

“…Previous electrophysiological studies of cultured hippocampal or cerebellar neurons have noted an increase in voltage-gated Ca 2ϩ current with age in culture (Meyers and Barker, 1989;Gruol et al, 1992;Basarsky et al, 1994;Randall and Tsien, 1995), but the time-dependent relationship of Ca 2ϩ current to cell death has not been studied directly or for the extended periods examined in the present study. The finding of a significant positive temporal correlation between Ca 2ϩ current density and neuronal death suggests that increased Ca 2ϩ current and cell death may be functionally related (Fig.…”

“…Critical developmental processes such as the appearance of neurotransmitters and ion channels, neurite outgrowth, synaptogenesis, and intrinsic firing patterns all depend in part on developmental changes in voltage-dependent C a 2ϩ conductances (Mattson and Kater, 1987;Gruol et al, 1992;Basarsky et al, 1994;Spitzer, 1994;Rusanescu et al, 1995;T urrigiano et al, 1995).…”

Differential Expression and Association of Calcium Channel α1B and β Subunits during Rat Brain Ontogeny

“…The dramatic changes that occur in calcium conductances during neuronal maturation suggest an underlying and equally dramatic change in the density and subtype of VDCC. Indeed, in cultured cerebellar Purkinje cells, studies have demonstrated that changes in calcium conductances were critical for neuronal maturation (53). More recently, important changes were observed in the expression and differential contribution of N-type and P/Q-type VDCC during synapse formation in cultured neurons (30 -32).…”