Transmembrane channels have been found in the membrane fraction of corn (Zea mays W64AN) mitochondria that exhibit a remarkable resemblance to the voltage dependent anion-selective channels (VDAC) located in the outer membrane of animal (Rattus norvegicus), protist (Paramecium aurelia), and fungal (Neurospora crassa) mitochondria.The channels in corn were demonstrated to be essentially identical to VDAC channels in three characteristic properties: (a) single channel conductance magnitude, (b) weak anion selectivity, and (c) nature of voltage dependence. These findings led us to conclude that the channels present in corn mitochondria are VDAC channels. This discovery may have repercussions concerning the regulation and function of higher plant mitochondria, and the causation of higher plant excitability.Mitochondria have an inner and an outer membrane. The inner membrane is known to be involved (among other functions) in the processes of cellular respiration, and the generation of ATP. In contrast, the exact function of the outer membrane is not as well understood. Early research on the outer membrane of isolated mitochondria indicated that the outer membrane is freely permeable to molecules as large as several thousand daltons (17,19, 26, 27). In animals (Rattus norvegicus), protists (Paramecium aurelia), and fungi (Neurospora crassa), the permeability ofthe outer mitochondrial membrane has been demonstrated to be due to large transmembrane protein channels, which form 3 to 4 nm in diameter aqueous pathways through the membrane (2,10,12,24). These channels are distinguished from all other channels by their location in the outer membrane of mitochondria, and by three characteristic properties: (a) the magnitude of their single channel conductance, (b) their weak anion selectivity, and (c) the nature of their voltage dependence (4,11,24 (2,4,7,23,24). They are referred to as being voltage dependent because the probability of which state the channels will be in at a given instant in time is a function of the voltage difference across the membrane containing them (2,4,7,23,24). The VDAC channels are also anion selective since they preferentially allow anions to pass through them as opposed to comparably sized and charged cations (3,24). 'Supported by National Institutes of Health grant No. GM28450.2 Abbreviation: VDAC, voltage dependent anion-selective channels.In higher plants, negatively stained outer mitochondrial membranes have been examined by EM. Points of stain with average center to center spacings of 4.5 nm were observed (18). Channels have been extracted from mung bean mitochondrial outer membranes whose pore size is very similar to VDAC channels (28). These findings suggest that there are large transmembrane channels in the outer membrane of higher plant mitochondria. A study of these channels could prove to be quite interesting since all mitochondria examined to date have been shown to possess VDAC channels (2,4,7,23,24). Thus, any observed differences in properties between the channels in hig...