Six lumbar dorsal root ganglia were rapidly dissected and placed in Ham's F12 medium (Gibco BRL, Grand Island, NY, U.S.A.). Rats were fully anesthetized with an overdose of sodium pentobarbital (50 mg kg −1, i.p.) and then were killed by decapitation. Our results thus strongly suggest the presence of two functionally distinct components of the Na +/K + pump current in rat small DRG neurons.ĭRG neurons were obtained from the L4-6 segments of 8- to 14-week old male Sprague–Dawley rats (250–400 g body weight) using an enzymatic dissociation procedure as described previously ( Sanada et al., 2002). In the present study, we used small (⩽25 μm in soma diameter) DRG neurons of adult rat to investigate the properties of the Na +/K + pump current and found that ouabain inhibition as well as Na + activation for the Na +/K + pump current exhibit biphasic concentration–response relationship. The presence of α3 β1 isozymes of the Na +/K + ATPase in rat DRG neurons has yet to be fully elucidated, especially in small neurons. (1999b) have measured the membrane current produced by the activity of Na +/K + ATPase in rat DRG neurons and have shown that the Na +/K + pump current in small and large neurons is primarily generated by the Na +/K + ATPase isozyme having a low affinity for ouabain as expected for α1 β1 isozyme. Using the whole-cell patch-clamp method, Dobretsov et al. Previous transfection studies using single, defined α isoforms have demonstrated that rat α1 isoforms exhibit a higher affinity for intracellular Na + but a lower sensitivity to blockade by ouabain compared with α3 isoforms ( Munzer et al., 1994 Therien et al., 1996 Zahler et al., 1997 Abriel et al., 1999 Horisberger & Kharoubi-Hess, 2002). Immunocytochemical studies using isoform-specific antibody have revealed that α isoforms are differentially expressed in subpopulations of DRG neurons α1 isoform is equally expressed in small and large neurons, whereas the α3 isoform is predominantly distributed in large ones ( Dobretsov et al., 1999a). Previous in situ hybridization studies have shown that mRNAs for α1, α3 and β1 isoforms of the Na +/K + ATPase are expressed in rat DRG ( Mata et al., 1991 Fink et al., 1995), suggesting the existence of two isozymes of the Na +/K + ATPase namely, α1 β1 and α3 β1.
The DRG comprises functionally heterogeneous cell types and the size (diameter) of their soma closely correlates with their functions small neurons transmit nociceptive information whereas large ones are closely related to the transmission of tactile and proprinoceptive impulses ( Harper & Lawson, 1985).
CELL MEMBRANE NA K 3D SKIN
These α and β isoforms have been shown to be expressed in a species- and tissues-dependent pattern (for a review, see Blanco & Mercer, 1998).ĭorsal root ganglion (DRG) neurons transmit various types of sensory information from peripheral tissues such as muscle and skin to the spinal cord. To date, four α isoforms ( α1 – α4) and three β isoforms (β1 – β3) have been identified in mammalian tissues. The smaller β subunit has a molecular weight of about 55 kDa and is necessary for the structural and functional maturation of the α subunit ( Hasler et al., 1998 Abriel et al., 1999). Thus, the catalytic, transport and pharmacological properties of the Na +/K + ATPase are generally considered to reside in its α subunit. The α subunit exhibits a molecular mass of about 110 kDa and contains the binding site for ATP, Na +, K + and cardiac glycoside ouabain.
The Na +/K + ATPase is a heterodimer composed of an α-catalytic subunit with 10 membrane-spanning domains and a β-glycoprotein subunit with a single membrane-spanning domain (for review, see Sweadner, 1989 Blanco & Mercer, 1998). The steep gradients of these ions are essential for regulating the osmotic balance and for maintaining the resting membrane potential and excitable properties in electrically active cells such as neurons and muscles. The Na +/K + ATPase or electrogenic Na +/K + pump transports three Na + out of the cell and two K + into the cell by using the energy derived from hydrolysis of one molecule of ATP and thereby plays a crucial role in maintaining the Na + and K + gradients across the plasma membrane.
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