Preheat oven to 350°.
Combine first 5 ingredients in a medium bowl; stir well.
Lightly spoon flours into dry measuring cups; level with a knife. Combine flours, sugar, soda, and salt in a large bowl; make a well in center of mixture. Add buttermilk mixture; stir just until moist. Spoon batter into 12 muffin cups coated with cooking spray. Bake at 350° for 20 minutes or until a wooden pick inserted in center comes out clean. Remove from pans; cool on a wire rack.